The present invention relates to a container with a flange obtained by heat-molding a sheet provided with a thermoplastic polyester layer, and to a method of producing the same. More specifically, the invention relates to a polyester container with a flange having improved impact resistance and heat resistance in the lower part of the barrel thereof and having superior transparency.
Thermoplastic polyesters such as polyethylene terephthalate and the like have excellent impact resistance, heat resistance and transparency as well as a certain degree of gas barrier property, and have been widely used for producing a variety of kinds of packaging containers.
Such packaging containers can be represented by a container with a flange obtained by molding a stretched or unstretched thermoplastic polyester sheet.
Japanese Unexamined Patent Publication (Kokai) No. 53852/1984 discloses a method of producing a transparent container by monoaxially stretching a thermoplastic resin sheet while maintaining the reduction ratio of the width of the sheet to be not larger than 10% and heat-molding the thus obtained monoaxially oriented sheet (prior art 1).
Japanese Examined Patent Publication (Kokoku) No. 27850/1989 discloses a method of heat-molding a polyester sheet by molding a biaxially stretched polyester sheet having a crystallinity of not larger than 30% and an index of surface orientation of from 0.02 to 0.15 by utilizing the compressed air along a mold heated at a temperature which is not higher than the crystallizing temperature (Tcxc2x0 C.) of the polyester but is not lower than (Tcxe2x88x9270)xc2x0 C., heat-treating the obtained molded article by bringing it into contact with the heated mold, fitting a cooling mold to the heating mold, the cooling mold having a shape nearly corresponding to the heating mold, forcibly transferring the molded article toward the cooling mold side from the heated mold side by blowing the compressed air, and cooling the molded article upon contact with the cooling mold (prior art 2).
Japanese Examined Patent Publication (Kokoku) No. 36534/1992 discloses a polyester container having a heat-adhering portion that can be thermally adhered to the closure member, the container being obtained by molding a polyester sheet containing a polyethylene terephthalate as a chief constituent component, the heat-adhering portion having a crystallinity of smaller than 20%, and the bottom portion and(or) the side portion of the container having the crystallinity of not smaller than 20%, the container being useful as an ovenable tray (prior art 3).
Japanese Patent No. 2947486 discloses a method of producing a biaxially stretched thermoplastic product by forming a biaxially stretched intermediate product by blow-molding a sheet-like thermoplastic material in a tube at a stretching temperature while preventing the material from adhering to the top of the side walls, placing the intermediate product on a male mold of a preset size and a texture, heating the intermediate product and the mold at a temperature higher than the temperature for stretching the thermoplastic material so that the intermediate product is thermally shrunk on the surface of the mold, cooling the intermediate product that is thermally shrunk, and taking the thermally shrunk intermediate product out of the mold (prior art 4).
The prior art 1 uses a monoaxially stretched sheet as the sheet for molding. This molding method may be capable of improving the transparency of the container but still leaves room for improvement concerning the heat resistance of the container.
The prior art 2 uses a biaxially stretched sheet as the sheet for molding. This molding method may be capable of improving the heat resistance of the container but is not still satisfactory concerning the impact resistance of the container.
These prior arts 1 and 2 use a sheet that has been stretched in advance as the sheet to be molded and, hence, require a particular stretching step and, hence, an additional cost. It is therefore desired to use an unstretched sheet and to impart, in a step of forming the container, the molecular orientation that is desired from the standpoint of imparting the container properties. It is further desired that the properties such as heat resistance, impact resistance and transparency are imparted in the steps of molding the container without requiring any particular step.
According to the prior art 3, an amorphous polyester sheet that is heated and plasticized is formed into a tray by using a metal mold maintained at a crystallizing temperature in order to heat-crystallize the bottom portion and/or the side portion. However, there is no disclosure concerning molecularly orienting the side portion by stretching, and it is considered that the container that is obtained is still insufficient with respect to impact resistance and transparency.
The prior art 4 is to produce a final container by preparing a biaxially stretched intermediate product by the blow-molding and by heat-shrinking the intermediate product on the male mold. This method, however, requires both heating for heat-shrinking the intermediate product on the male mold and cooling for shaping the heat-shrunk intermediate product and for taking it out. Therefore, this method is not still satisfactory from the standpoint of thermal economy, extended periods of time occupying the molds and low productivity.
It is therefore an object of the present invention to provide a container with a flange exhibiting excellent heat resistance and impact resistance in the lower part of the barrel portion and excellent transparency in the container wall despite it is obtained by molding an amorphous polyester sheet, and a method of producing the same.
Another object of the present invention is to provide a heat-resistant thermoplastic resin container having a novel profile of crystallinities in that the side wall portion of the container comprises oriented crystals, and the outer surface of the side wall has a crystallinity larger than that of the inner surface of the side wall, and a method of producing the same.
A further object of the present invention is to provide a method of producing a thermoplastic resin container, having split functions of effecting the heat-set by a female mold and effecting the cooling by a plug, shortening the time for occupying the mold and enhancing the productivity.
A still further object of the present invention is to provide a sheet-molded container having excellent heat resistance, impact resistance and transparency not only in the side wall of the container but also in the central portion on the bottom of the container despite the container is obtained by molding an unoriented or amorphous thermoplastic polyester sheet, and a method of producing the same.
According to the present invention, there is provided an impact resistant container obtained by heat-molding a sheet provided with a thermoplastic polyester layer comprising chiefly an ethylene terephthalate unit, and having a flange portion, a barrel portion and a closed bottom portion, the wall of the lower part of the barrel portion being oriented and crystallized so as to possess a crystallinity of not smaller than 15% as measured by the density method, and the wall of the barrel portion being oriented to satisfy the following formulas (1), (2) and (3),
Iu(xe2x88x92110)/Iu(010)xe2x89xa61.02xe2x80x83xe2x80x83(1)
IL(xe2x88x92110)/IL(010)xe2x89xa60.89xe2x80x83xe2x80x83(2)
and
(Iu(xe2x88x92110)/Iu(010))xe2x88x92(IL(xe2x88x92110)/IL(010))xe2x89xa70.13xe2x80x83xe2x80x83(3)
wherein Iu(xe2x88x92110) is a diffraction intensity of the surface having an index of a plane of (xe2x88x92110) in the upper part of the wall of the barrel portion of when an X-ray is incident on the wall surface of the container perpendicularly thereto and when the axial direction of the container is regarded to be a perpendicular of the optical coordinate, Iu(010) is a diffraction intensity of the surface having an index of a plane of (010) in the upper part of the wall of the barrel portion of when an X-ray is incident on the wall surface of the container perpendicularly thereto and when the axial direction of the container is regarded to be a perpendicular of the optical coordinate, IL(xe2x88x92110) is a diffraction intensity of the surface having an index of a plane of (xe2x88x92110) in the lower part of the wall of the barrel portion of when an X-ray is incident on the wall surface of the container perpendicularly thereto and when the axial direction of the container is regarded to be a perpendicular of the optical coordinate, and IL(010) is a diffraction intensity of the surface having an index of a plane of (010) in the upper part of the wall of the barrel portion of when an X-ray is incident on the wall surface of the container perpendicularly thereto and when the axial direction of the container is regarded to be a perpendicular of the optical coordinate,
as measured by the X-ray diffraction by using a curved PSPC microdiffractometer.
In the container of the present invention, the ratio (H/R) of the height (H) of the barrel portion to the inner diameter (R) at the top of the barrel portion is desirably in a range of from 0.8 to 2.0 for fulfilling the object of the invention. Further, the flange portion may have a crystallinity of smaller than 10% as measured by the density method, or the flange portion may have a crystallinity of not smaller than 20% as measured by the density method.
According to the present invention, there is further provided a method of producing an impact resistant container by heating a sheet provided with an amorphous thermoplastic polyester layer comprising chiefly an ethylene terephthalate unit at a sheet temperature (Ts) that satisfies the following formula (4),
Tg less than Ts less than Tg+50xc2x0 C.xe2x80x83xe2x80x83(4)
wherein Tg is a glass transition point of the thermoplastic polyester,
and molding and heat-setting the sheet by using a plug having a bottom area of not smaller than 70% of the bottom area of the container and a plug temperature (Tp) that satisfies the following formula (5),
Tgxe2x88x9230xc2x0 C. less than Tpxe2x89xa6Tg+30xc2x0 C.xe2x80x83xe2x80x83(5)
wherein Tg is the glass transition point of the thermoplastic polyester,
in one step or in two steps in a metal mold with a plug-assisted compressed air or vacuum.
In the production method of the present invention, it is desired that the metal mold has a temperature (Tm) that satisfies the following formula (6),
Tgxe2x89xa6Tmxe2x80x83xe2x80x83(6)
wherein Tg is a glass transition point of the thermoplastic polyester.
Further, the plug may be an ordinary plug or a plug having a stepped shoulder for forming a flange.
According to the present invention, further, there is provided a heat-resistant resin container obtained by molding a thermoplastic polyester sheet, at least the side wall of the container being oriented and crystallized due to stretching, and the side wall of the container having a crystallinity which is larger in the outer surface thereof than in the inner surface thereof.
In the heat-resistant resin container of the present invention, it is desired that:
1. The container has a flange portion, a side wall portion and a bottom portion, and the ratio (H/D) of the height (H) of the container to the diameter (D) of the container is not smaller than 0.5;
2. The flange portion of the container is cloudy and the side wall is transparent when it contains no pigment; and
3. A change in the volume of the container is not larger than 1.0% after it is heat-treated in an oven at such a temperature that the side wall portion thereof is maintained at 90xc2x0 C. for 3 minutes.
According to the present invention, further, there is provided a method of producing a heat-resistant resin container by molding a thermoplastic resin sheet into the shape of a female mold heated at a temperature higher than the crystallization temperature of the resin by the compressed air, followed by heat-setting and, then, reducing the pressure in the molded article so that the molded article shrinks into the shape of a plug having the shape of a final container to impart the shape thereto, followed by cooling.
In the method of producing the heat-resistant resin container of the present invention, it is desired that:
1. A primary molded article obtained by stretching the thermoplastic resin sheet by using a plug is molded with the compressed air;
2. The thermoplastic resin sheet is an amorphous sheet of a thermoplastic polyester;
3. The plug has a surface area wider by more than three times than the area to be molded of the thermoplastic resin sheet; and
4. The temperature of the plug is not lower than the glass transition point of the thermoplastic resin but is lower than the temperature of the female mold.
The method of producing the heat-resistant resin container of the present invention can be put into practice even by a one-step molding method or by a two-step molding method.
In the two-step molding method, it is desired that the thermoplastic resin sheet is stretched and molded by using a plug for stretch-molding prior to applying the compressed air, and the obtained primary molded article is supported by a shape-imparting plug in a separate step to effect the molding with the compressed air and the shrinking. In this case, further, it is desired that the temperature of the shape-imparting plug is not higher than the glass transition point of the thermoplastic resin.
According to the present invention, further, there is provided a method of producing a heat-resistant container by preparing an intermediate article by heat-shrinking a pre-molded article obtained by solid-phase-molding the sheet provided with an amorphous thermoplastic polyester layer, molding the intermediate product with the compressed air in a female metal mold for final molding heated at a temperature higher than the crystallization start temperature of said polyester, heat-setting the molded article, reducing the pressure inside the molded article so that the molded article shrinks along the outer surface of the plug having the shape of the final container to impart the shape thereto, followed by cooling.
In the embodiment of the present invention, it is desired that the sheet is solid-phase-molded by pressing the sheet by using a plug for pre-molding, the sheet being clamped by a clamping metal mold and a female mold for pre-molding, and by supplying the pressurized gas to between the sheet and the plug. In molding the sheet in this case, it is desired that the sheet temperature is maintained to lie between the glass transition point (Tg) of the thermoplastic polyester +15xc2x0 C. and the glass transition point +40xc2x0 C., that the plug is maintained at a temperature between the glass transition point xe2x88x9230xc2x0 C. and the glass transition point +20xc2x0 C., and that the female mold for pre-molding is maintained at a temperature between the glass transition point of the thermoplastic polyester +10xc2x0 C. and the glass transition point +50xc2x0 C.
In the present invention, further, it is desired that the pre-molded article is supported by a plug for intermediate molding and is inserted in the female mold for intermediate molding, and the molded article is caused to shrink along the outer surface of the plug to impart the shape thereto followed by cooling. In this case, it is desired that the female mold for intermediate molding is maintained at a temperature in a range of not lower than the crystallization start temperature, that the plug for intermediate molding is maintained at a temperature lower than the temperature of the female mold for intermediate molding and in a range of from 80 to 110xc2x0 C., and that the surface area of the pre-molded article is from 1.1 to 1.5 times as large as the surface area of the intermediate article.
According to the present invention, further, it is desired that the female mold for final molding is maintained at a temperature of not lower than the crystallization start temperature of the thermoplastic polyester, and that the plug for the final container is maintained at a temperature in a range of from the glass transition point of the thermoplastic polyester xe2x88x9220xc2x0 C. to the glass transition point +20xc2x0 C.
According to the present invention, there is further provided a container having excellent heat resistance and impact resistance obtained by stretching and molding a thermoplastic polyester, the thermoplastic polyester in the bottom portion of the container having a crystallinity of not smaller than 15%, and the center in the bottom portion of the container being substantially transparent and having a distinguished diffraction peak in the surface of an index of a plane (010) in the X-ray diffraction.
In the container of the present invention, it is desired that:
1. The oriented crystallization tendency (U) as defined by the following formula (I),
U=H(010)/H(xe2x88x92110)xe2x80x83xe2x80x83(I)
wherein H(010) is a diffraction intensity of the surface having an index of a plane (010) in the X-ray diffraction, and H(xe2x88x92110) is a diffraction intensity of the surface having an index of a plane (xe2x88x92110) in the X-ray diffraction,
is not smaller than 1.3 at the center in the bottom portion;
2. The sheet having the thermoplastic polyester layer is stretched and molded in the solid phase; and
3. The crystallinity of the thermoplastic polyester in the side wall of the container is not smaller than 15%.